Methods, systems, and apparatus for intelligent lighting

ABSTRACT

An ambient light sensor measures an ambient light level at one point in an illuminated environment, such as a warehouse, office, shop, cold-storage facility, or industrial facility, and provides an indication of the measured ambient light level to a processor. The processor maps the measured ambient light level to an estimated ambient light level at a different point in the illuminated environment from the measured ambient light level (e.g., a “task height” about three feet from a warehouse floor). The processor may determine the difference between the estimated ambient light level and a desired light level at the task height, and may change the artificial illumination provided by a light fixture to make the actual ambient light level at task height match the desired light level at the task height.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §111(a) toInternational Patent Application PCT/US2012/063372, filed Nov. 2, 2012,which in turns claims the priority benefit of U.S. Provisional PatentApplication No. 61/555,075, filed on Nov. 3, 2011, under Atty. DocketNo. 099431-0143, entitled “Methods, Apparatus, and Systems forIntelligent Lighting,” and of U.S. Provisional Patent Application No.61/577,354, filed on Dec. 19, 2011, under Atty. Docket No. 099431-0144,entitled “Methods, Systems, and Apparatus for Daylight Harvesting,” bothof which applications are hereby incorporated herein by reference.

BACKGROUND

Intelligent lighting systems combine solid-state light sources, embeddedsensors and controls, and low-cost pervasive networking to create anintegrated illumination system which is highly responsive to itsenvironment. Benefits of some or all such systems may include, but arenot limited to, a much higher quality of light tailored specifically touser needs and significant energy savings, compared to legacy lightingsystem technologies.

In many environments illuminated by artificial light, significantamounts of ambient daylight may be present at certain times of the day.When sufficient levels of ambient light are present, intelligentlighting systems may reduce the amount of artificial light delivered inorder to maintain consistent environmental lighting conditions and tosave energy. The process of changing the amount of light emitted by afixture in response to changes in ambient lighting conditions is knownas “daylight harvesting.”

Conventional lighting fixtures are typically arranged in groups, each ofwhich is on a single circuit. When a detector (or a person) senses thatthe ambient light level has risen above a predetermined threshold in agiven part of the warehouse, the sensor (or person) triggers a switchthat turns off an entire circuit. Similarly, if the ambient light levelfalls below a predetermined threshold, the circuit may be turned on toprovide additional light.

SUMMARY

Embodiments of the present invention include a lighting fixture toilluminate an environment and a corresponding method of illuminating theenvironment, such as a warehouse, a cold-storage facility, an officespace, a retail space, an educational facility, an entertainment venue,a sports venue, a transportation facility, and a correctional facility.An exemplary lighting fixture includes a memory, an ambient lightsensor, a processor communicatively coupled to the memory and theambient light sensor, and a light source, such as a light-emitting diode(LED), communicatively coupled to the processor. The memory stores afirst transfer function mapping first ambient light levels at a firstposition within the environment to corresponding second ambient lightlevels at a second position within the environment. The ambient lightsensor measures an actual ambient light level at the first positionwithin the environment. The processor determines: an expected ambientlight level at the second position, based on the actual ambient lightlevel measured at the first position and the first transfer functionstored in the memory; and a change in a light output of the lightingfixture to provide a desired ambient light level at the second position,based at least in part on the expected ambient light level at the secondposition. And the light source generates the change in the light outputof the lighting fixture so as to provide the desired ambient light levelat the second position.

In certain embodiments, the first position is at the lighting fixtureand the second position is at a task height within the environment(e.g., about 1 ft to about 6 ft from the floor of the environment).

The memory may be configured to store a plurality of transfer functions,including the first transfer function, each of which maps ambient lightlevels at the first position within the environment to correspondingambient light levels at the second position within the environment. Eachof these transfer functions may correspond to a different state of theenvironment. In such cases, the lighting fixture may also include acommunications interface to accept a user input selecting the firsttransfer function from among the plurality of transfer functions and/ora state parameter sensor to provide a state parameter measurement usedby the processor to select the first transfer function from among theplurality of transfer functions. For instance, the lighting fixture mayinclude a real-time clock, communicatively coupled to the processor,that provides a timing signal used by the processor to select the firsttransfer function from among the plurality of transfer functions.

The processor may also be configured to determine a portion of theactual ambient light level provided by the lighting fixture (artificiallight) and/or a portion of the actual ambient light level provided byone or more light sources (daylight) other than the lighting fixture.For example, the ambient light sensor may sense a wavelength of at leastone spectral component of the actual ambient light level, and theprocessor may determining the amount of artificial light and/or daylightin the actual ambient light based on the wavelength sensed by theambient light sensor.

The processor may control the light source to generate the change in thelight output of the lighting fixture so as to provide the desiredambient light level at the second position. For instance, the processormay adjust the intensity, beam pattern, direction, color, and/or a colortemperature of the light output.

An exemplary lighting fixture may also include an occupancy sensor,communicatively coupled to the processor, that senses a presence of atleast one occupant within the environment and provides an occupancysignal indicative of the at least one occupant. The processor may selectthe desired ambient light level at the second position within theenvironment based at least in part on the occupancy signal. In addition,the occupancy sensor may sense a number of occupants within theenvironment, a location of the at least one occupant within theenvironment, and/or a motion of the at least one occupant within theenvironment.

Additional embodiments include a sensing module and corresponding methodof calibrating a sensing module. (Such a sensing module may beintegrated into or communicatively coupled to a lighting fixture orballast interface.) An exemplary sensing module includes an ambientlight sensor, a memory, and a processor communicatively coupled to theambient light sensor and to the memory. The ambient light sensorgenerates an actual output representative of a change in an actualambient light level of the environment caused by a change in a lightoutput of at least one light source illuminating the environment. Thememory stores a transfer function mapping ambient light levels of anenvironment to corresponding outputs of the ambient light sensor. Andthe processor determines (1) an expected output of the ambient lightsensor based on the transfer function stored in the memory and thechange in the ambient light level and (2) a difference between theactual output and the expected output. The processor also updates thetransfer function stored in the memory based on the difference betweenthe actual output and the expected output.

An exemplary sensing module may also include a communications interface,communicatively coupled to the processor, to transmit a signal thatcauses the at least one light source to generate the change in the lightoutput. In addition, the processor may log, in the memory, the output,the expect output, and the change in the light output of the at leastone light source illuminating the environment.

Yet another embodiment includes a ballast interface for a light-emittingdiode (LED) lighting fixture and a corresponding method of operating aballast interface. The ballast interface includes a power input, an LEDdriver circuit, a power meter operatively coupled to the power input,and a power management unit (PMU) communicatively coupled to the powermeter. The power input receives alternating current (AC) power. The LEDdriver circuit transforms the AC power to power suitable for driving atleast one LED in the LED lighting fixture. The power meter senses awaveform of the AC power. And the PMU adjusts the LED driver circuit inresponse to the waveform of the AC power.

In some cases, the power meter measures a phase angle, a power factor,and/or a noise level of the AC power. The PMU may determine a presenceof at least one of a brownout and a lightning strike based on thewaveform of the AC power. The PMU may a current drawn by the LED drivercircuit to power the at least one LED in response to the waveform of theAC power. The PMU and/or the power meter may also store a representationof the waveform of the AC power in a memory.

For purposes of the present disclosure, the term “ambient light” refersto visible radiation (i.e., radiation whose wavelength is between about450 nm and about 700 nm) that pervades a given environment or space. Inother words, ambient light is the soft, indirect light that fills thevolume of the environment and is perceptible to a person within theenvironment.

Similarly, the term “ambient light level” refers to the illuminance, orluminous flux on a surface per unit area. The illuminance is a measureof how much the incident light illuminates the surface,wavelength-weighted by the luminosity function to correlate with humanbrightness perception. Luminous flux may be measured in lux (lumens persquare meter) or foot-candles.

The following U.S. published applications are hereby incorporated hereinby reference:

U.S. Pat. No. 8,232,745, filed Apr. 14, 2009, and entitled “MODULARLIGHTING SYSTEMS”;

U.S. Pat. No. 8,138,690, filed Jun. 25, 2010, and entitled “LED-BASEDLIGHTING METHODS, APPARATUS, AND SYSTEMS EMPLOYING LED LIGHT BARS,OCCUPANCY SENSING, LOCAL STATE MACHINE, AND METER CIRCUIT”;

U.S. Pre-Grant Publication No. 2010-0296285-A1, published Nov. 25, 2010,filed Jun. 17, 2010, and entitled “SENSOR-BASED LIGHTING METHODS,APPARATUS, AND SYSTEMS EMPLOYING ROTATABLE LED LIGHT BARS”;

U.S. Pre-Grant Publication No. 2010-0301773-A1, published Dec. 2, 2010,filed Jun. 24, 2010, and entitled “LED-BASED LIGHTING METHODS,APPARATUS, AND SYSTEMS EMPLOYING LED LIGHT BARS OCCUPANCY SENSING, ANDLOCAL STATE MACHINE”;

U.S. Pre-Grant Publication No. 2010-0302779-A1, published Dec. 2, 2010,filed Jun. 24, 2010, and entitled “LED-BASED LIGHTING METHODS,APPARATUS, AND SYSTEMS EMPLOYING LED LIGHT BARS, OCCUPANCY SENSING,LOCAL STATE MACHINE, AND TIME-BASED TRACKING OF OPERATIONAL MODES”;

U.S. Pre-Grant Publication No. 2010-0264846-A1, published Oct. 21, 2010,filed Jun. 28, 2010, and entitled “POWER MANAGEMENT UNIT WITH ADAPTIVEDIMMING”;

U.S. Pre-Grant Publication No. 2010-0295473-A1, published Nov. 25, 2010,filed Jun. 30, 2010, and entitled “LED LIGHTING METHODS, APPARATUS, ANDSYSTEMS INCLUDING RULES-BASED SENSOR DATA LOGGING”;

U.S. Pre-Grant Publication No. 2010-0301768-A1, published Dec. 2, 2010,filed Jun. 30, 2010, and entitled “LED LIGHTING METHODS, APPARATUS, ANDSYSTEMS INCLUDING HISTORIC SENSOR DATA LOGGING”;

U.S. Pre-Grant Publication No. 2010-0270933-A1, published Oct. 28, 2010,filed Jun. 30, 2010, and entitled “POWER MANAGEMENT UNIT WITH POWERMETERING”;

U.S. Pre-Grant Publication No. 2012-0235579, published Sep. 20, 2012,filed Mar. 20, 2012, and entitled “METHODS, APPARATUS AND SYSTEMS FORPROVIDING OCCUPANCY-BASED VARIABLE LIGHTING”;

U.S. Pre-Grant Publication No. 2012-0143357, published Jun. 7, 2012,filed Nov. 4, 2011, and entitled “METHOD, APPARATUS, AND SYSTEM FOROCCUPANCY SENSING”;

WO 2012/061709, published May 10, 2012, filed Nov. 4, 2011, and entitled“METHOD, APPARATUS, AND SYSTEM FOR OCCUPANCY SENSING”; and

WO 2012/129243, published Sep. 27, 2012, filed Mar. 20, 2012, andentitled “METHODS, APPARATUS AND SYSTEMS FOR PROVIDING OCCUPANCY-BASEDVARIABLE LIGHTING.”

It should be appreciated that all combinations of the foregoing conceptsand additional concepts discussed in greater detail below (provided suchconcepts are not mutually inconsistent) are contemplated as being partof the inventive subject matter disclosed herein. In particular, allcombinations of claimed subject matter appearing at the end of thisdisclosure are contemplated as being part of the inventive subjectmatter disclosed herein. It should also be appreciated that terminologyexplicitly employed herein that also may appear in any disclosureincorporated by reference should be accorded a meaning most consistentwith the particular concepts disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The skilled artisan will understand that the drawings primarily are forillustrative purposes and are not intended to limit the scope of theinventive subject matter described herein. The drawings are notnecessarily to scale; in some instances, various aspects of theinventive subject matter disclosed herein may be shown exaggerated orenlarged in the drawings to facilitate an understanding of differentfeatures. In the drawings, like reference characters generally refer tolike features (e.g., functionally similar and/or structurally similarelements).

FIGS. 1A and 1B illustrate an intelligent lighting fixture withintegrated ambient light sensing and occupancy sensing, according to oneembodiment of the present invention.

FIG. 2A illustrates a typical warehouse environment illuminated by alighting fixture, according to one embodiment of the present invention.

FIG. 2B shows one possible distribution of lighting fixtures andskylights in a typical warehouse environment, according to oneembodiment of the present invention.

FIG. 3A is a diagram of a tunable ambient light sensor feeding directlyinto a software-configurable daylight harvesting control state machinesystem, according to one embodiment of the present invention.

FIG. 3B is a state diagram for a state machine suitable forimplementation by the daylight harvesting control state machine systemof FIG. 3A.

FIG. 4 is a flow diagram that illustrates how to select and maintain adesired ambient light level using a transfer function relating theambient light level at task height L_(f) to the sensor value V_(s),according to one embodiment of the present invention.

FIG. 5A is a plot of the sensor value V_(s) versus the ambient lightlevel at the sensor position L_(s) for different environments andlighting fixtures, according to one embodiment of the present invention.

FIG. 5B is a plot of the ambient light level at task height L_(f) versusambient light level at the sensor position L_(s) for differentenvironments and lighting fixtures, according to one embodiment of thepresent invention.

FIG. 5C is a plot of a transfer function that maps the ambient lightlevel at task height L_(f) to the sensor value V_(s) for differentenvironments and lighting fixtures, according to one embodiment of thepresent invention.

FIG. 6 illustrates a relationship between ambient light present in anenvironment and ambient light sensor signal value, for several values ofa typical “tuning” parameter (e.g., sensor gain), according to oneembodiment of the present invention.

FIG. 7A is a plot that shows pairs of sensor readings and light outputsas a function of the light output 4 of an intelligent lighting fixture,according to one embodiment of the present invention.

FIG. 7B is a scatter plot of sensor values and light outputs, includingthose shown in FIG. 8A, for an intelligent lighting fixture, accordingto one embodiment of the present invention.

FIG. 8 is a plot that illustrates of energy consumption cost with andwithout daylight harvesting, according to one embodiment of the presentinvention.

FIG. 9 is a diagram of a microcontroller-based power management unitconfigured to perform various power and energy measurement functions,according to one embodiment of the present invention.

DETAILED DESCRIPTION

Following below are more detailed descriptions of various conceptsrelated to, and embodiments of, inventive systems, methods and apparatusfor intelligent lighting related to daylight harvesting, temperaturemonitoring, and power analysis. It should be appreciated that variousconcepts introduced above and discussed in greater detail below may beimplemented in any of numerous ways, as the disclosed concepts are notlimited to any particular manner of implementation. Examples of specificimplementations and applications are provided primarily for illustrativepurposes. For instance, although FIGS. 2A and 2B illustrate an inventivelighting fixture 100 in a warehouse environment, those of skill in theart will readily appreciate that inventive lighting fixtures andtechniques may be deployed in any suitable environment, including, butnot limited to cold-storage facilities, office spaces, retailenvironments, sports venues, schools, residential areas, outdoor spaces,correctional facilities, and industrial facilities.

In many environments illuminated by intelligent lighting systems,real-time collection of ambient temperature data at many points providesvaluable insight into the performance of other building systems, such asHVAC systems, machinery of various sorts, and high-volume chillersystems for cold storage environments. Intelligent lighting systems withintegrated temperature sensing functionality can provide this real-timedata stream to facilitate analysis, monitoring, and adjustment of theseother building systems.

Many intelligent lighting systems also feature the ability to measureand analyze the energy used by the various parts of the lighting system.This measurement may occur at the facility level, at the level of anindividual electrical circuit within the facility, or at the level of anindividual light fixture within an electrical circuit. Measuringcharacteristics of energy and power used by individual light fixturesprovides significant end-user benefits in both accuracy and granularityof analysis.

Embodiments of the present disclosure include sn apparatus fordetermining a first ambient light level at a first position (e.g., aboutone foot to about six feet from a floor). In an illustrative embodiment,the apparatus includes a sensor to measure a second ambient light levelat a second position (e.g., at a lighting fixture) and a processor,which is operably coupled to the sensor, to determine the first ambientlight level based on the second ambient light level. The processor maybe further configured to determine a difference between the secondambient light level and a desired light level and, optionally, todetermine a change in an illumination level to bring the first ambientlight level into coincidence with the desired light level. In at leastone example, the processor is further configured to adjust anillumination level to bring the first ambient light level intocoincidence with the desired light level and to drive a light source,which is operably coupled to the processor, to provide illumination atthe illumination level. An exemplary apparatus may also include acommunications interface that is operably coupled to the processor andconfigured to provide an indication of the second ambient light level toa lighting fixture or another processor.

Other disclosed embodiments include methods of determining a differencebetween a first ambient light level and a desired ambient light level.Exemplary methods include measuring a second ambient light level at asecond position, determining the first ambient light level based on thesecond ambient light level, and determining a difference between thefirst ambient light level and the desired light level. Further exemplarymethods may also include adjusting an illumination level to bring thefirst ambient light level into coincidence with the desired light level.

Intelligent Lighting Fixtures

FIGS. 1A and 1B depict an illustrative lighting fixture 100 thatilluminates an environment with light output from one or more light bars120, each of which includes one or more light-emitting diodes (LEDs)that emit white light (and/or light at discrete wavelengths or bands inthe visible spectrum) to illuminate the environment. The LEDs on thelight bars 120 may be turned on and off individually in groups and/orset different to light levels as understood in the art. Similarly, thelight bars 120 may be rotated or pointed so as to illuminate differentsections of the environment, e.g., using a motor, gimbal mount, spindle,or other suitable mechanism. Those of skill in the art will also readilyappreciate that other inventive lighting fixtures may include more orfewer light bars 120, longer or shorter light bars 120, and/or otherlight sources, such as incandescent bulbs, arc lamps, or fluorescentbulbs.

The LED light bars 120 are mounted to a frame 102 that also holds anambient light sensor 110, a ballast interface or power management unit(PMU) 130, an occupancy sensor 140, and one or more status LEDs 190,which indicate the lighting fixture's current operating mode (e.g.,active mode, sleep mode, service mode), whether or not the lightingfixture 100 needs to be serviced, whether the lighting fixture 100 iscommunicating with another device, etc. As shown in FIG. 1B, thelighting fixture 100 and/or the PMU 130 may include or be coupled to oneor more LED drivers 122, a hardware power meter 150, a low-voltage powersupply 152, a high-voltage power supply 154, a communications interface160 coupled to an antenna 162, a real-time clock 170, and a temperaturesensor 180. The lighting fixture 100 may include other components aswell, such as a battery, back-up transmitter, “wired” communicationsinterface, and additional sensors.

Each of these components is communicatively coupled to the PMU 130,e.g., via an appropriate bus or electrical connection, and may be amodular component that can be “hot swapped” or replaced in the field orintegrated into either the lighting fixture 100 or the PMU 130.Alternatively, one or more of these components may be packagedseparately and installed apart from the lighting fixture 100 or the PMU130 and communicatively coupled to the lighting fixture 100 or PMU 130,e.g., via a wireless interface.

As described in greater detail below, the PMU 130 controls theillumination emitted by the LEDs on the LED light bars 120. FIG. 1Bshows that the PMU 130 includes processor 132, such as a microprocessor,microcontroller, field-programmable gate array (FPGA), or other suitableprocessing device. The PMU 130 also comprises a non-transitory,nonvolatile memory 134, depicted in FIG. 1B as an electrically erasableprogrammable read-only memory (EEPROM). The memory 134 iscommunicatively coupled to the processor 132 (e.g., via an appropriatebus or connection) and stores processor-implementable instructions inthe form of software and/or firmware for controlling the light output ofthe LED light bars 120. These instructions may take the form of rulesthat dictate how the processor 132 implements a state machine (describedbelow) and rules for transitioning among states of the state machine.

The PMU 130 logs measurement signals (data) in the memory 134 from theambient light sensor 110, occupancy sensor 140, hardware power meter150, communications interface 160, and real-time clock 170 and may causethe state machine to transition from one state to another state based onthese measurement signals. For instance, the processor 132 may cause thelight output of the LED light bars 120 to change in response to inputsfrom the ambient light sensor 110, occupancy sensor 140, temperaturesensor 180, and/or real-time clock 170 according to the instructionsstored in the memory 134. These components, their respective functions,and the other components shown in FIG. 1B are described in greaterdetail below.

Ambient Light Sensors

The ambient light sensor 110 may be a photocell (e.g., an Intersil™ISL29102 Low Power Ambient Light-to-Voltage Non-Linear Converter) thatmonitors the level of ambient light at the sensor position or sensorheight, L_(s), emits an ambient light signal whose value (e.g.,amplitude or phase), V_(s), represents the amount of detected ambientlight. The ambient light sensor 110 may include one or more opticalelements (e.g., a lens) that direct ambient light onto one or morephotosensitive elements, which transduce incident photons into aphotocurrent, voltage, change in resistance, or other measureableelectrical quantity. The ambient light sensor 110 may also include acircuit that provides automatic gain control—that is, the circuitcontrols the proportionality of the signal V_(s) to the measured ambientlight level L_(s). If desired, the sensor gain can be tuned (eithermanually, automatically, or via remote control), e.g., to increase ordecrease the ambient light sensor's sensitivity to ambient light.Similarly, the sensor circuit may include an offset that can beincreased or decreased, e.g., to account for changes in fixed-patternbackground illumination or noise.

In one example, an illustrative ambient light sensor 110 may employprocessor-based tuning of the light sensor gain, offset, and thresholdcharacteristics for improving the accuracy and precision of ambientlight measurement. In some cases, the ambient light sensor 110 may betuned after installation in a target environment to account for specificambient light characteristics of that environment, such as thereflectivity of various surfaces, location and brightness of windows,skylights, or other light sources, or desired ambient light levels atvarious locations in that environment. The tuning process may beautomated, or may involve substantial manual interaction. The tuningprocess may be conducted via a software user interface or via aspecial-purpose handheld device. The tuning process may be a one-timeoperation, or may be repeated (manually or automatically) to account forchanges in the target environment.

An exemplary ambient light sensor 110 may respond to light in thevisible, near infrared, mid-infrared, and far-infrared portions of theelectromagnetic spectrum. For instance, the light sensor 110 may includetwo active regions: a first active region that senses visible light anda second active region that senses infrared light. Light sensors whichmeasure both visible light and infrared light may output the visible andinfrared readings separately to allow an intelligent lighting controllerto distinguish between the ambient light provided by the sun (whichcontains a significant infrared component) and the light provided by anartificial light source (which may contain little or no infraredcomponent). These readings may allow a controller (e.g., the statemachine implemented in the PMU 130) to maintain target illuminationlevels and prevent undesired feedback loops in the PMU 130 from drivingthe daylight harvesting system as explained below.

Occupancy Sensors

The occupancy sensor 140 monitors the illuminated environment for thepresence of people, vehicles, etc., and transmits an occupancy signal tothe PMU 130 when it detects a person, vehicle, moving object, etc. inthe illuminated environment. As understood by those of skill in the art,the occupancy sensor 140 may be a passive infrared (PIR) device thatoperates by sensing infrared radiation emitted by a person (or animal)in the environment. The occupancy sensor 140 may also emitradio-frequency or ultrasonic pulses and detect echo pulses reflectedfrom objects or people in the environment. The occupancy sensor 140 maybe configured to detect a person's location within the environment. Itmay also sense the number of people within the environment, theirrespective locations within the environment, and their respectivetrajectories within or through the environment.

As shown in FIG. 1B, the occupancy sensor 110 is operably coupled to thememory 134 (shown in FIG. 1B as an electrically erasable programmableread-only memory (EEPROM)) via a filter 142, an amplifier 144, amulti-bit analog-to-digital converter (ADC) 146, and a processor 132.The filter 144 removes noise from an analog occupancy signal generatedby the occupancy sensor 140, and the amplifier boosts the filteredoccupancy signal's strength. The ADC 146 digitizes the amplifiedoccupancy signal, and the processor 132 uses the digitized occupancysignal to determine the light output of the LED light bars 120. Theprocessor 132 may also store some or all of the digitized occupancysignal in the memory 134.

When the occupancy sensor 140 detects an occupancy event (e.g., a personentering a previously unoccupied room), it may increase the amplitude ofits output (the occupancy signal). The processor 132 receives thisoccupancy signal and treats it as a state parameter indicative of theenvironment's occupancy state (e.g., occupied or unoccupied). If theoccupancy signal indicates that the environment is occupied, then theprocessor 132 may send a signal to one or more LED drivers 122, whichrespond to the signal by changing the amount of light emitted by one ormore LED light bars 120. As described below, the processor 132 maydetermine the desired output of the LED light bars based at least inpart on a transfer function selected based on the occupancy signalitself as described in greater detail below.

The processor 132 may continue transmitting a “high” occupancy signal tothe LED drivers 122 for as long as the occupancy sensor 110 detects anoccupancy event, or it may send a second signal to the LED drivers 122in response to detection of another change in occupancy (e.g., when theoccupancy event ends). Alternatively, the processor 132 may simply sendan occupancy signal periodically for as long the occupancy state of theenvironment does not change. At this point, the lighting fixture 100enters a delay or timeout period, based on instructions stored in thememory 134 and timing data from the clock 170, during which the LEDlight bars 120 remain in the active state (or possibly transition to astate of intermediate activity, e.g., 50% illumination). Once the delayperiod has elapsed, as indicated by the change in state of a signal fromthe processor 132 and/or the LED driver 122, the LED light bars 120enter an inactive state (e.g., they turn off or emit light at a very lowlevel). As described below, the processor 132 may adjust the delayperiod and/or the light levels based on its analysis of logged sensordata.

Additional State Parameter Sensors

The lighting fixture 100 may also include additional state parametersensors, each of which may be integrated into the PMU 130 orcommunicatively coupled to the PMU 130 via an appropriate communicationsinterface. For instance, the lighting fixture 100 and/or the PMU 130 mayinclude one or more temperature sensors 180 to sense the temperature ofthe lighting fixture 100, its components (e.g., the LEDs in the LEDlight bars 120), and/or the ambient temperature (the temperature of theair surrounding the lighting fixture 100). The lighting fixture 100and/or the PMU 130 may also include an radio-frequency identification(RFID) sensor (not shown) for tracking RFID tags, a magnetometer, acamera, and any other sensor suitable for sensing a state of theenvironment. These additional sensors (not shown) may be coupled to theprocessor 132 via one or more digital input/output ports 164 and/or oneor more analog input ports 166 or integrated into the lighting fixture100 and/or the PMU 130.

The lighting fixture 100 also includes a real-time clock 170 that canalso, optionally, be integrated into the PMU 130. The real-time clock170 provides timing data (e.g., time-stamp information) on an as neededor periodic basis to the processor 132, which may store or tag thesensor data (including the ambient light and occupancy data) in thememory 134 with time stamps to indicate when the data was collected. Inaddition, the processor 132 may treat the time stamps as stateparameters that indicate the time of day, day of the week, or day of theyear. If the processor 132 determines from the time stamp that it is aweekend day or a holiday, it may determine that, for a given occupancycondition, the ambient light level should be lower that the ambientlight level for a weekday at the same time. It may also determine thatan intruder is present or that a security breach has occurred based onoccupancy event data detected when the facility is closed. The real-timeclock 170 may also be used to time or coordinate the sensor/lightingfixture delay period and to synchronize the PMU 130 to other devices,systems, and components on the same network and/or within the sameenvironment.

Ambient Light, Occupancy Sensor Data, and Daylight Harvesting StateMachines

The PMU 130 may use ambient light sensor data and/or occupancy sensordata to advance a software-configurable state machine governing thelight fixture's behavior. More specifically, the PMU 130 may employambient light and occupancy measurements to “harvest” light from othersources, including the sun, to reduce the lighting fixture's lightoutput and energy consumption. As part of this process, the PMU 130 maydetermine the light output from the light bars 120 using a“fixture-to-task” transfer function that maps the ambient light levelsmeasured at the ambient light sensor 110 to the ambient light levels at“task position” or “task height,” which correspond to the position orheight at which a person working in the environment engages in tasksbenefiting from illumination. For instance, task height may be theheight at which a person uses his or her hands at a desk, in/on a rack,or holds a clipboard. In a warehouse, cold-storage facility, or officeenvironment, task position or task height may about 1 ft to about 6 ftfrom the ground, e.g., about 3, 4, or 5 ft. An environment may includemultiple task heights or task positions; for example, in a warehousefull of racks, there may be a different task position associated witheach rack in the warehouse and/or each rack in a shelf.

In many situations, the ambient light sensor 110 may be located somedistance from the task position or task height. For instance, theambient light sensor 110 may be suspended from the ceiling as part ofthe fixture 100 in a high-bay or mid-bay installation or mounted to thewall as part of a separate sensor unit or PMU 130. As a result, theambient light level at the sensor may be different than the ambientlight level at the task position/height. To compensate for this, the PMU130 may use a “fixture-to-task” transfer function, stored in the memory134 (e.g., as a look-up table), that maps the measured ambient lightsignal from the ambient light sensor 110 to the estimated ambient lightlevel at task position/height. The PMU 130 uses this transfer function,together with information about the lighting fixture's light output, todetermine the amount of daylight illuminating the environment and thechange in the lighting fixture's light output necessary to achieve adesired ambient light level at task height.

The PMU 130 may also update or calibrate the fixture-to-task transferfunction based on closed-loop feedback from the ambient light sensor 110and the PMU 130. In some cases, for example, the processor 132 may alsolog ambient light sensor data and information about the lightingfixture's light output in the memory 134 on a periodic basis to trackchanges in the environment's reflectivity over days, weeks, months, oryears. It may also log ambient light sensor data in the memory 134immediately before and after a change in the lighting fixture's lightoutput. From these measurements, the PMU 130 may determine that thetask-position ambient light level has not increased by the desiredamount and may change the lighting fixture's light output and thetransfer function's scaling accordingly.

Consider, for example, a lighting fixture 100 that illuminates thewarehouse environment shown in FIGS. 2A and 2B, with racks 12 arrangedon a floor 10 in an open (and possibly cavernous) space. One or moreskylights 14 (FIG. 2B) allow sunlight to illuminate correspondingsections of the warehouse. The amount of sunlight entering the warehousevaries with the time of day (angle of the sun) and the weather. Forinstance, a passing cloud may cast a shadow over the skylight, reducingthe amount of sunlight that enters the warehouse on an otherwise sunnyday. The amount of sunlight entering the warehouse may also vary withthe season, with more sunlight in the summer and less in the winter, andthe cleanliness of the skylights 14. Light from outside artificialsources, such as neon signs and security fixtures, as well asobstructions, such as other neighboring buildings, may also affect theamount of ambient light admitted by the skylights 14.

Variations in the amount of light coming through the skylights 14affects the ambient light level at task height L_(f), which may be aboutthree feet above the floor 10. Task height represents the height atwhich a worker in the warehouse performs day-to-day tasks, includinginspecting items (and tags on items), moving items on and off shelves onthe racks, turning switches on and off, and working with his or herhands. Obstructions scattered throughout the warehouse may attenuate,scatter, or reflect light from skylights 14, so the ambient light levelat task height may not necessarily be the same as the ambient lightlevel at other distances from the floor. The ambient light level at taskposition/height may also vary with (lateral) position on the floor(distance from a rack 12/skylight 14/window). For instance, a rack 12may shield one area of the warehouse floor 10 from light coming inthrough a particular skylight 14, but not another area.

One or more intelligent lighting fixtures 100 illuminate the warehouseenvironment. The lighting fixtures 100 may be mounted from the ceilingof the warehouse and arrayed in a semi-regular grid (e.g., along aislesbetween racks) as shown in FIGS. 2A and 2B, with the exact number andarrangement of lighting fixtures 100 depending on the desires and needsof the property manager and users. In some embodiments, the lightingfixtures 100 are communicatively coupled to each other (“networkedtogether”) via wireless or wired communication channels. For instance,the fixtures 100 may exchange information with each other via wirelessradio-frequency links, pulse-width modulated (PWM) infrared links,Ethernet links, wired link, or any other suitable communications link.(In some cases, the ambient light sensor 110 and/or occupancy sensor 140may receive data from other sensors/PMUs/fixtures via an infrared datalink.) The fixtures 100 may also be communicatively coupled to a server(not shown) or other processor that collects and processes usage andenvironmental data collected by sensors on the fixtures 100.

In operation, the PMU 130 in each lighting fixture 100 measures theambient light level on a continuous or periodic basis and senses thepresence (or absence) of occupants in the environment. Each PMU 130 alsomonitors aspects of the light emitted by its fixture 100, such as theintensity, direction, and pattern of the beam(s) projected by the LEDlight bars 120 into the environment. For instance, the PMU 130 maycompute the intensity of the emitted beam based on a measurement of thepower drawn by the LED driver circuit 122, the fixture's temperature andage, and information stored in the memory 134 about the operatingcharacteristics of the LED light bars 120. The PMU 130 uses thisinformation, along with ambient light level measurements and calibrationdata about the ambient light sensor 110, to determine what fraction ofthe measured ambient light is light emitted by the LED light bars 120and what fraction comes from other light sources, such as the sun. Itmay also measure the power spectral density of the ambient light todetermine how much sunlight is present, if any.

If the PMU 130 determines that the amount of sunlight is increasing, itmay cause the lighting fixture 100 to emit less light so as to maintaina desired ambient illumination level. Similarly, if the PMU 130determines that the amount of sunlight is decreasing, it may cause thelighting fixture 100 to emit more light so as to maintain the desiredambient illumination level. The PMU 130 may also cause the lightingfixture 100 to change the beam pattern in response to an indication thatone portion of the environment is brighter than another portion of theenvironment, e.g., because the sun is shining through one window orskylight but not another. For instance, the PMU 130 can selectively turnon or off LEDs in the LED light bars 120; cause some LEDs to emit morelight than others; modulate the transparency, focus, or pattern of anelectro-active optical element (e.g., a spatial light modulator) placedover some or all of the LEDs in a light bar 120; or actuate a motor thatrotates one or more of the LED light bars 120.

Occupancy-Based State Machine Employing a Fixture-to Task TransferFunction

In at least one embodiment, an inventive PMU 130 implements anoccupancy-based state machine that uses the “fixture-to-task” transferfunction described above to provide a desired task-position ambientlight level for a given occupancy state. Each occupancy state may haveassociated with it a desired task-position ambient light level, ortarget illumination level. In operation, the occupancy sensor 140detects a change in occupancy state and reports the change to the PMU130, which advances the state machine from one state to another (e.g.,unoccupied to occupied) based on the change. (It may also advance thestate machine based on signals from a timer, such as the real-time clock170.) The PMU 130 determines the target level for the new state andservos the lighting fixture's light output using ambient light sensordata and the “fixture-to-task” transfer function to compensate forchanges in daylight levels, environmental reflectivity, etc.

FIG. 3A shows a state machine 300 that maps the measured ambient lightlevel to a desired ambient light level according to the“fixture-to-task” transfer function described above. When the sensorvalue V_(s) increases (e.g., in response to an increase in the ambientlight level), the state machine may instruct the PMU 130 to cause theLED light bars 120 to emit less light or to turn off completely. Whenthe sensor value V_(s) decreases (e.g., in response to a decrease in theambient light level), the state machine may instruct the PMU 130 tocause the LED light bars 120 to turn on or emit more light. The statemachine 300 may also record and analyze readings from the ambient lightsensor 110 to “learn” appropriate light level settings for given sensorreadings V_(s) as described below.

FIG. 3A shows that the ambient light sensor 110 provides a raw analogsignal 111 representing the measured ambient light level L_(s) at thesensor to a filter and amplifier 302, which together transform the rawanalog signal 111 into a processed analog signal 113 by removingspurious spectral components from the signal and boosting the signalamplitude. An analog-to-digital converter (ADC) 304 coupled to thefilter and amplifier 302 converts the processed analog signal 113 to amulti-bit (e.g., 12-bit or 16-bit) digitized signal 115. The ADC 304provides the digitized signal to the state machine 300, which implementsa sensor tuning software module 306 and a daylight harvesting controlloop 308 to analyze and respond to the digitized signal 115 as well asto signals from the occupancy sensor 140 and from other signal sources(e.g., the real-time clock 170).

The sensor tuning software module 306 may also adjust the gain, offset,and threshold in response to measurements that map the ambient lightlevel L_(f) at task height to the instantaneous value V_(s) of thedigitized signal 115. For instance, the sensor tuning software module306 may change the sensor gain in response to changes in the sensor'sperformance or changes in the environment. Painting the walls of theenvironment or moving boxes on the racks 12 may cause the reflectivityto increase or decrease by a known or measureable amount. Tuning thesensor gain, offset, and/or threshold compensates for this change inreflectivity.

FIG. 3B illustrates a state diagram 350 for the state machine 300implemented by the PMU 130. In some embodiments, the daylight harvestingcontrol loop 308 determines and controls the light provided by thelighting fixture 100 by transitioning among the states shown in thestate diagram 350. For instance, the state machine's default state maybe an inactive state 352 in which the lighting fixture 100 emits nolight or only a minimal amount of light, e.g., for safety purposes. Uponreceiving an indication of an occupancy event 354 (e.g., the entrance ofa person into the environment) from the occupancy sensor 140, thecontrol loop 308 transitions the lighting fixture 100 from the inactivestate 352 to an active occupied state 356. For instance, the controlloop 308 may increase the lighting fixture's light output to provide atarget illumination level (stored in the memory 134) for the activeoccupied state 356 according to ambient light sensor data and thefixture-to-task transfer function (also stored in the memory 134).

The lighting fixture 100 remains in the active occupied state 356 solong as the environment remains occupied. In the active occupied state356, the control loop 308 may servo the light output setting about adesired (e.g., constant) value of the ambient light level L_(f) at taskheight using proportional-integrative-derivative (PID) control with gaincoefficients tuned to provide the desired response. Those of skill inthe art will readily appreciate that other forms of control (e.g.,proportional control or proportional-derivative control) may be employedas well.

In some environments, and with some sensors 110, this can beaccomplished when the control loop 408 that implements a “laggyfollower,” i.e., PID control where the “proportional” gain coefficientis equal to the reciprocal of the error term. The control loop 308 mayalso provide an “asymmetric” response to changes in the ambient lightlevels: it may increase the light output setting quickly in response toa decrease in the ambient light level and decrease the light outputgradually in response to an increase in the ambient light level. Thetype of response may also vary with user commands, the time of day, thetime of year, the weather, the presence or absence of people in or nearthe illuminated environment, etc. Similarly, the desired ambient lightlevel at task height L_(f) may be constant or may vary in response touser commands, the time of day, the time of year, the weather, thepresence or absence of people in or near the illuminated environment,etc.

When occupancy is no longer detected (358), the control loop 308transitions the lighting fixture 100 from the active occupied state 356to an active unoccupied state 360, e.g., by starting a sensor delaytimer 362 controlled by the real-time clock 170. The lighting fixture100 remains in the active unoccupied state 360 until the sensor delaytimer 362 elapses, in which case the control loop 308 transitions thelighting fixture 100 to the inactive state 352, or the occupancy sensor140 detects another occupancy event 354, in which case the control loop308 transitions the lighting fixture 100 to the active occupied state356.

Transfer Functions Mapping Ambient Light Levels to Light Outputs

As explained above, the PMU 130 uses the fixture-to-task transferfunction to map the measured ambient light level to an estimated ambientlight level, and a state-to-target transfer function to map thefixture's current operating state to a desired ambient light level foreach state of the environment. These transfer functions may be stored inlook-up tables as one or more combinations of measured ambient lightlevel(s), current lighting fixture light output(s), and change(s) inlighting fixture light output to achieve a particular ambient lightlevel. In one example, the PMU 130 determines the amount of lightprovided by other sources (the amount of “daylight”) by subtracting ascaled or calibrated measure of the lighting fixture's light output fromthe measured ambient light level. It may also determine the amount ofdaylight by measuring the power spectral density of the ambient lightand decomposing the measured power spectral density into the weightedsuperposition of the power spectral densities of the sun and thelighting fixture.

The PMU 130 also determines the target ambient light level, or desiredillumination level, based on an occupancy signal from the occupancysensor 140 and, optionally, time values from the real-time clock 170 oranother time source. For instance, the target illumination level may behighest during daytime hours when the environment is occupied, highduring nighttime hours when the environment is occupied, and low whenthe environment is unoccupied. If the target ambient light level ishigher than the measured ambient light level, or if the amount ofdaylight decreases, the PMU 130 increases the light output of thelighting fixture 100. If the target ambient light level is lower thanthe measured ambient light level, or if the amount of daylightincreases, the PMU 130 decreases the light output of the lightingfixture 100.

The PMU 130 also updates the target ambient light level if theenvironment's state changes, e.g., according to the state diagram 350 inFIG. 3B. In some examples, the memory 134 stores different transferfunctions (look-up table) for different environmental configurations.These environmental configurations may be defined in terms of user input(e.g., via the communications interface 160) and/or state parametersthat are sensed or measured by the various sensors integrated into orcommunicatively coupled to the PMU 130 (e.g., the number of people orobjects within the ambient light sensor's field of view). For instance,the presence of many pallets in the environment may reduce theenvironment's reflectivity, which in turn affects the transfer function.Likewise, weekly (or monthly) cleaning may increase the environment'sreflectivity. Other factors that may affect the fixture-to-task transferfunction include but are not limited to: the number of occupants withinthe environment, spatial distribution of occupants within theenvironment, activity (motion) of the occupants, light output of thelighting fixture, time of day, day of the week, time of the year,ambient temperature, fixture temperature, operational status of thelighting fixture, operational status of other lighting fixtures in theenvironment, and age of the lighting fixture.

FIG. 4 is a flow chart that illustrates a process 400 executed by thePMU 130 to select, use, and update a fixture-to-task transfer function424 that maps measured ambient light levels to estimated ambient lightlevels based on the state of environment illuminated by the lightingfixture 100. The process 400 includes four sub-processes: anoccupancy-based state machine sub-process 410; an ambient light levelsub-process 420; an adjustment sub-process 430; and a “learning”sub-process 440. Together, sub-processes 420 and 430 form a first(inner) closed feedback loop that servos the light output to maintainthe target illumination level, and sub-processes 420, 430, and 440 forma second (outer) closed feedback loop to adjust the transfer function424.

In the occupancy-based state machine sub-process 410, the occupancysensor 140 senses or measures the occupancy state 414 of theenvironment. The PMU 130 combines this occupancy data with timer data412 from the real-time clock to advance an operating state machine 416from one state to another according to operating rules stored in thememory 134. (The PMU 130 may also use information about temperature,time of day, day of the week, operational status of the lightingfixture, etc. to advance the state machine.) For instance, the PMU 130may receive an occupancy signal from the occupancy sensor 140 indicatingthat the environment has transitioned from an unoccupied state to anoccupied state. The PMU 130 determines the environment's operating state417 and selects a target illumination level 419 at task heightcorresponding to the operating state 417 from a look-up table (LUT) 418stored in the memory 134.

In the ambient light level sub-process 420, which may occur before,during, or after execution of the state machine sub-process 410, the PMU130 receives a measurement of the ambient light level 422 (possibly inhexadecimal form) from the ambient light sensor 110 and records thismeasurement in the memory 134. (The PMU 130 may log the state parametersin the memory 134 as well.) It maps this measured ambient light level atone location to the estimated ambient light level at the task locationaccording to the fixture-to-task transfer function 424, possibly bydetermining the amount of daylight as well. This mapping yields apredicated task-height ambient light level 426, which the PMU comparesto the target illumination level 419 at task height (comparison 450).

In the adjustment sub-process 430, which may run continuously oriteratively (e.g., periodically), the PMU 130 calculates the error 432between the predicted ambient light level 434 at task height and thetarget illumination level 419 at task height (comparison 450). It uses acontrol loop 434, such as a proportional-integral-derivative (PID)control loop, to adjust the output of the lighting fixture 100 (step436) so as to provide the desired amount of illumination. As understoodby those of skill in the art, the PID control loop 434 generates aweighted sum of the present error, the accumulation of past errors, anda prediction of future errors to generate an adjustment amount to thelighting fixture's light output so as to keep the measured ambient lightlevel 322 at a level corresponding to the target illumination level 419at task height.

The “learning” sub-process 440 involves monitoring the inner controlloop (sub-processes 420 and 430) (step 442) and updating thefixture-to-task transfer function (step 444), e.g., using logged sensordata and/or the calibration routines described below. In thissub-process 440, the PMU 130 compares the measured ambient light level422 to the target ambient light level 419, e.g., on a continuous,periodic, or intermittent basis. If the PMU 130 determines that thechanged ambient light level matches the target ambient light level, itresumes monitoring the ambient light level and the occupancy. Otherwise,if the PMU 130 determines that the changed ambient light level does notmatch the target ambient light level, it adjusts the transfer function(step 444) to compensate for the discrepancy between the measured andtarget values. For example, if the changed ambient light level is lowerthan the target ambient light level, the PMU 130 may adjust the transferfunction so as to increase the lighting fixture's light output for thestate of the environment, the amount of daylight, and the measuredambient light level. Likewise, if the changed ambient light level ishigher than the target ambient light level, the PMU 130 may adjust thetransfer function so as to decrease the lighting fixture's light outputfor the state of the environment, the amount of daylight, and themeasured ambient light level. The PMU 130 may use the sensormeasurements logged in the memory 134 to determine how much to changethe transfer function and, optionally, to determine whether or not thediscrepancy between measured and target light levels is spurious. If thediscrepancy is spurious, the PMU 130 may not adjust the transferfunction.

The ambient light level measurements 422 and occupancy statemeasurements 412 may occur continuously or at discrete intervals. Forinstance, they may occur periodically (e.g., once per second),aperiodically, and/or on demand They may occur more frequently when theenvironment is likely to be occupied, e.g., during operational hours.They may be synchronized or may occur asynchronously (e.g., the ambientlight level measurements 422 may occur more frequently than theoccupancy state measurements 412).

Mapping Sensor Readings to Ambient Light Levels at Task Height

Referring again to FIG. 3A, the state machine 300 may also map the valueV_(s) of the sensor signal to the amount of ambient light present attask height L_(f), which may be about three feet off of the floor 10,and adjusts the light output of the LED light bars 120 based on theamount of ambient light present at task height L_(f). The state machine300 may use the sensor reading V_(s) to keep L_(f) at desired levelunder some or all ambient lighting conditions. To do this, the statemachine 300 exploits the relationships among the ambient light levelL_(s) and L_(f) and the sensor reading V_(s) illustrated in FIGS. 5A-5C.In some cases, the state machine 300 maps the sensor reading V_(s) tothe ambient light level at the sensor L_(s), and the ambient light levelat the sensor L_(s) to the ambient light level at task height L_(f).These mappings may vary from sensor to sensor, and from environment toenvironment as explained below.

FIG. 5A shows the sensor reading V_(s) as a function of the ambientlight level L_(s) measured by two different exemplary ambient lightsensors 110 (sensors 1 and 2). Sensors 1 and 2 responds differently tothe same amount of ambient light L_(s) due to variations in their gain,offset, and threshold setting as well differences in theirmanufacturing. For instance, the optical coupling between the lenses andthe sensing elements may be lossier in one sensor than in the other,possibly due to imperfections in the lenses or index-matching fluid usedto optically mate the lenses to the sensing elements. In addition, eachsensing element may generate a different amount of current (or voltage,or change in resistance, etc.) in response to a given irradiance. Ifdesired, the differences between sensors can be reduced by tuning thegain, offset, and threshold of each sensor appropriately, e.g., usingthe gain curves shown in FIG. 6. Alternatively, the relationship betweenthe sensor reading V_(s) and the ambient light level L_(s) for a givensensor can be measured (e.g., before or after installation) and usedwhen processing sensor readings V_(s).

FIG. 5B illustrates how the ambient light level at the sensor L_(s)relates to the ambient light level L_(f) at task height for two notionalenvironments—in this case, a more reflective environment (environment 1)and a less reflective environment (environment 2). In both environments,light reflected or scattered off the floor and other surfaces propagatesfrom task height to the ambient light sensor 110. The color, roughness,and orientation of the surfaces within the environment affect how muchlight scatters or reflects off the surfaces in the environment to theambient light sensor 110. The proximity of the ambient light sensor 110to windows, skylights, and other light sources may also affect therelationship between the ambient light level at the sensor L_(s) relatesto the ambient light level L_(f) at task height.

Plotting the ambient light level L_(s) at the sensor versus the ambientlight level L_(f) at task height yields the curve shown in FIG. 5B.Multiplying the values plotted in FIG. 5B (Ls as a function of L_(f))with the values plotted in FIG. 5A (V_(s) as a function of L_(s)) yieldsthe values plotted in FIG. 5C (V_(s) as a function of L_(f)). FIG. 5Cshows how the sensor reading V_(s) relates the ambient light level attask height L_(f). The state machine 300 and PMU 130 may use datarepresenting this relationship to determine how much light the lightingfixture 100 should emit to keep the ambient light level at task heightL_(f) at a desired level given a sensor reading. For instance, the statemachine 300 may access a look-up table in the memory 134 that includescombinations of V_(s)/L_(f) values and corresponding illuminationsettings for desired values of ambient light level at task height L_(f).

Manual Transfer Function/Ambient Light Sensor Calibration

In some cases, the relationship shown in FIG. 5B may be determinedempirically after installation of the ambient light sensor 110 in theenvironment. During commissioning of the lighting fixture 100, forexample, a user may set all ambient light to be constant or choose amoment when the ambient light level is relatively constant. Next, theuser sets the fixture 100 to a known brightness level (e.g., 100%illumination) and measures the ambient light level L_(f) at task heightwith a separate sensor, such as a handheld photodetector, while theambient light sensor 110 measures the ambient light level L_(s) at thesensor. Then the user sets the fixture 100 to a different brightnesslevel (e.g., no illumination) and measures the ambient light level L_(f)at task height with the separate sensor while the ambient light sensor110 measures the ambient light level L_(s) at the sensor. The user maymeasure the ambient light level L_(f) at task height as many times andat as many different illumination levels as desired. Additionalmeasurements may be averaged or used to provide more points forcurve-fitting confidence. (Alternatively, the sensor 110 can infer theambient light level at task height L_(f) from measurements of lightlevels at sensor height L_(s) as described below.)

Automatic Transfer Function/Ambient Light Sensor Calibration

FIGS. 7A and 7B illustrate an alternative process for determining therelationship between sensor reading V_(s) and ambient light level attask height L_(f) for a given ambient light sensor 110 in a givenenvironment. A user installs the lighting fixture 100, then sets it tooperate in response to user commands or according to default settingsderived from estimates or a priori knowledge of the sensor/environmentrelationship. As the lighting fixture 110 operates, it changes theillumination levels in response to occupancy events (e.g., it may turnon when someone enters the environment and turn off or dim after atimeout period following the most recent occupancy event), the time ofday (e.g., it may turn off or dim automatically at night), and theambient lighting conditions. Just before and just after the lightingfixture 100 switches between lighting levels (dims or brightens), theambient light sensor measures the ambient lighting level L_(s). Thefixture 110 records the measurements of ambient lighting levels L_(f) asa function of fixture light output in a memory.

FIG. 7A shows six pairs of such measurements: A and B, C and D, and Eand F. The sensor 110 makes each pair of measurements quickly, so theamount of light detected from sources other than the lighting fixture110 remains relatively constant over each measurement interval. As aresult, subtracting the “low” measurement (e.g., measurement A) from the“high” measurement (e.g., measurement B) in each pair of measurementsyields the change in sensor reading V_(s) for a given change in thelight output setting of the lighting fixture 100.

Plotting these measurements (along with many other before-and-aftermeasurements) yields the scatter plot shown in FIG. 7B. Because thechange in the light output setting is known (the PMU 130 commands thechange in light output setting), each pair of measurements can be usedto determine a slope that represents the sensor's response to changes inthe light output setting, which correlates with the ambient light levelL_(s). Fitting a curve 702 to the plotted points (e.g., using a simplelinear fit or a least squares fit to a polynomial function) yields therelationship between the sensor reading and the light output settings(and/or ambient light levels L_(s)). The state machine 300 may storeindications of this relationship in memory as points in a LUT orcoefficients of an equation that defines the shape of the curve 702.

The relationship between sensor readings V_(s) and light output settingsrepresented by the curve 702 in FIG. 7B can be used to map the sensorreadings V_(s) to the ambient task-height ambient light level L_(f)based on one or more measurements of the task-height ambient light levelL_(f) for a given sensor reading V_(s). In one example, the statemachine 300 uses a single measurement of the task-height ambient lightlevel L_(f) for a given sensor reading V_(s) to fix the curve 702 withrespect to a desired ambient light level at task height. The pairs ofsensor readings provide the slope m of the curve 702, and the ambientlight measurement provides the offset b, to provide a solution to theequation L_(f)=mV_(s)+b. The state machine 300 may then servo the lightoutput setting about the corresponding sensor reading V_(s) to providethe desired level of illumination.

The state machine 300 may continue to measure and record pairs of sensorreadings V_(s) as the lighting fixture operates, e.g., on a periodicbasis, an as-needed or as-desired basis, or even every time the lightingoutput setting changes. The state machine 300 can use these additionalmeasurements to update the sensor reading/light output settingrelationship represented by the curve 702 in FIG. 7B and to adjust thelight output setting due to degradations or other changes in thesensor's behavior or the fixture's behavior caused by age, temperature,and other factors. If the state machine 300 has a model of therelationship between the ambient lighting level at task height L_(f) andthe sensor reading V_(s) (i.e., a model of the transformation that mapsV_(s) to L_(f)), it may also be able to update its model in response tochanges in the environment that affect the sensor readings V_(s). Forinstance, painting the walls of a warehouse or moving products aroundinside a warehouse may increase the reflectivity, which, in turn,increases the amount of ambient light at task height for a given lightoutput setting and a given amount of sunlight. This causes the averagesensor reading V_(s) to increase for a given light output, all otherfactors being equal. The state machine 300 may alert the PMU 130 to sucha change, and the PMU 130 may adjust the light output settingsaccordingly.

The state machine 300 may utilize ambient light sensor data alone orcombined with occupancy sensor data; for instance, it may be asoftware-configurable state machine 300 that governs the behavior of oneor more individual light fixtures 100 based on a combination ofoccupancy and ambient light data. This software-configurable controlmay, for example, allow a user to specify one daylight harvestingprofile to be used when an occupancy sensor indicates the presence of aperson or vehicle in an area of interest and another daylight harvestingprofile to be used when the occupancy sensor indicates that the area isempty or inactive. In this example, the “inactive” daylight harvestingprofile may be configured to save more energy than the “active” profile.If no occupancy sensor data is available, a lighting control systemwhich uses ambient light sensor data may allow a user to specify atarget illumination level as well as maximum and minimum fixture dimminglevels, among other user-specifiable operating parameters.

Performance with Transfer-Function-Based Daylight Harvesting

FIG. 8 is a plot of energy used by an illustrative lighting fixture 100in an exemplary environment versus time of day with and without daylightharvesting. Without daylight harvesting, energy consumption isrelatively low at night and jumps dramatically during the day while thelighting fixture emit lights. With daylight harvesting, however, thelighting fixture energy consumption drops for most of the day. This isbecause the lighting fixture emits less light during the day than atnight thanks to effective measurement and exploitation of daylight. Thelighting fixture's energy consumption rises slightly above the nighttimelevel in the late afternoon and early evening, possibly due the earlieronset of dusk in early fall (October 3), when these data were collected.In the summer time (e.g., mid-July), the energy consumption may riselater in the evening as daylight hours lengthen, and in the winter(e.g., mid-January), the energy consumption may rise earlier in theevening as dusk sets in earlier.

Fault Detection and Protection with a Power Management Unit

An exemplary intelligent light fixture 100 may include an integratedpower and energy measurement subsystem that provides a detailed recordof power and energy usage over time. This power and energy usage may befurther broken down by fixture subsystem or individual driver outputchannels. It may also represent power and energy usage for the fixture100 as a whole. The power and energy management subsystem may alsomeasure characteristics of the AC power input to the light fixture,including but not limited to: phase angle, noise on the AC line, orpower factor. The power and energy management subsystem may logmeasurements in memory onboard the light fixture, or transmitmeasurements to a remote monitoring system via wired or wirelessnetwork.

Referring again to FIG. 1B, the integrated power and energy measurementsubsystem includes a hardware power meter 150 that is coupled to the PMU130 and receives alternating current (AC) power (e.g., 120 VAC at 60 Hz)from an AC power input 156. The hardware power meter 150 provides theprocessor 132 with metering data representing the amount and rates ofpower consumption as a function of time. A low-voltage power supply 152coupled to the power meter 150 transforms the AC power into low-voltage(e.g., 5 V) direct-current (DC) power suitable for running the processor132 and/or other low-voltage electrical components in the lightingfixture. A high-voltage power supply 154 coupled to the power meter 150transforms the AC power into high-voltage DC power suitable for runningthe LED driver 140 and the LED light bars 142. The low-voltage powersupply 152 and/or the high-voltage power supply 154 may filter and/orotherwise condition the AC power as desired.

Alternatively, the lighting fixture 100 (and occupancy sensing unit 102)may draw power from an external DC power supply, such as a rechargeablebattery. Such an embodiment may include one or more DC-DC powerconverters coupled to a DC power input and configured to step up or stepdown the DC power as desired or necessary for proper operation of theelectronic components in the lighting fixture 100 (and occupancy sensingunit 102). For instance, the DC-DC power converter(s) may supply DCvoltages suitable for logic operations (e.g., 5 VDC) and for poweringelectronic components (e.g., 12 VDC). In such embodiments, the powermeter 150 may

The processor 132 may use information derived from the power meter'smeasurements to identify various fault conditions and to protect thelighting fixture 100 and its components from some or all of these faultconditions. The power meter 150 may provide various power-relatedmeasurements to the microcontroller, including but not limited to: theinput AC voltage or current waveforms, the current or voltage waveformsassociated with energy storage capacitors, the output pulse duration ofa buck or boost power conversion circuit, or the voltage across andcurrent through a series-wired string of LEDs. For example, the powermeter 150 may sample the AC waveform received from the AC power input156 at a rate equal to or greater than the Nyquist frequency of the ACwaveform (e.g., a sampling rate of 120 Hz or higher for 120 VAC at 60Hz). The processor 132 may process these measurements to produce acalculated power measurement corresponding to each of several LED driveroutputs, to an entire light fixture, or to any or all of severalelectrical subsystems within a fixture. The processor 132 may also logsome or all of these samples in the memory 134 for later analysis, e.g.,to determine energy usage, lighting fixture performance, componentperformance, and/or performance of the corresponding circuit in the ACpower grid.

The processor 132 may also detect undesired fluctuations in the inputvoltage in real-time. The processor 132 may react to these fluctuationsin such a way as to prevent permanent damage to the fixture's powercontroller circuit, LEDs, or other electrical subsystems. The processor132 may also be configured to detect any of several possible failuremodes for the one or more strings of output LEDs and safely react to thefailure modes in a way that prevents permanent damage to the fixture'spower controller circuit, LEDs, or other electrical subsystems.

For instance, the processor 132 may determine whether the AC waveform'samplitude exceeds or falls below a predetermined threshold or exhibits apredetermined pattern or profile. If the processor 132 senses that theAC waveform's amplitude is drifting towards or has drifted below apredetermined threshold (e.g., 60 Vpp), the processor 132 may determinethat a brownout is occurring. In such a case, the processor 132 mayreduce power consumption by high-voltage components, such as the LEDlight bars 120, so to prevent these components from drawing too muchcurrent as the input voltage falls. Similarly, if the processor 132senses a sudden voltage spike, it may determine that a lightning strikehas occurred and shunt power and/or turn off one or more components inthe PMU 130 or lighting fixture 100. The processor 132 may also detectand respond to indications that one or more components within the PMU130 or fixture 100 is malfunctioning.

FIG. 9 illustrates additional power control circuitry in an exemplaryPMU 130. As described above, the PMU 130 includes a microcontroller(processor) 132, which can be used to implement the state machine 300 ofFIG. 3, coupled to a power controller 908 via a serial bus 906 thatisolates the processor 132 from the power controller 908. Upon receivinga new commanded power output (light output setting) from themicrocontroller 904, the power controller 908 adjusts the current, pulsewidth modulation, voltage, etc. provided by one or more LED drivers 910to the LED light bars 120. If one or more LEDs in the LED light bar 120fails, the LED drivers 910 sends a failure detection signal to the powercontroller 910, which may adjust the settings of the working LEDsaccordingly. The power controller 908 also provides indications of thedelivered power output, power controller status, LED driver status, andpower quality metrics to the processor 132.

Independent Power Management Units and Communications Interfaces

As shown in FIGS. 1B and 9, the lighting fixture 100 also includes acommunications (network) interface 160 coupled to the processor 132.This interface 160 may be incorporated into the PMU 130 if desired. Thecommunications interface 160, which is coupled to an antenna 162,provides the PMU 130 with access to a wireless communications network,such as a local area network or the Internet. The PMU 130 may transmitraw or processed occupancy data and/or ambient light data to a networkeddatabase, other lighting fixtures, or other occupancy sensing units viathe communications interface 160. It may also receive occupancy data,ambient light data, firmware or software updates, predictedenvironmental data (e.g., temperature and ambient light level data),commissioning information, or any other suitable information from othersources, e.g., other lighting fixtures, occupancy sensing units, orexternal controllers.

The ambient light sensor 110 and the occupancy sensor 140 can also serveas receivers for modulated infrared data from remote control devices,infrared beacons, or other data transmitters. Light sensors may alsoserve as receivers for modulated infrared or visible light data. Thisdata may be transmitted from a handheld device used in the sensor tuningprocess. This data may also be transmitted from an infrared or visiblelight beacon device attached to persons, vehicles, or other objects inthe environment to facilitate tracking of these objects as they movewithin the environment.

Alternative embodiments of the PMU may physically be detached orseparated from the lighting fixture. For instance, the PMU may bepackaged and deployed in the environment as an independent unit thatincludes integrated sensors (e.g., ambient light level sensor and/oroccupancy sensor) and a wired or wireless communications interface.Alternatively, or in addition, the PMU may be communicatively coupled toother PMUs, other light fixtures (including “dumb” light fixtures),and/or other independent sensors distributed throughout the environment.Such an independent PMU may detect ambient light levels and stateparameter information from integrated sensors and/or fromcommunicatively coupled sensors and process this data as describedabove. For instance, an independent PMU may be communicatively coupledto and control several lighting fixtures disposed to illuminate anenvironment. The PMU may also be retrofit to existing light fixtures,such as high-bay lighting fixtures common in many warehouses andcold-storage facilities.

Temperature-Based Intelligent Lighting

Inventive aspects of the temperature monitoring systems include, but arenot limited to, light fixtures 100 with integrated sensors (e.g.,temperature sensor 180 in FIG. 1B) to monitor the temperature of the airsurrounding the fixture while filtering out temperature changes due tothe operation of the fixture itself, remote temperature sensors designedto be integrated into an intelligent lighting system, and lightingcontrol systems capable of monitoring, analyzing, and displaying datafrom a grid of temperature sensors.

An intelligent light fixture 100 may include one or more integratedtemperature sensors 180 coupled to or integrated into its powermanagement unit (PMU 130 in FIGS. 1A, 1B, and 9). These sensors maymeasure temperature inside and/or outside of the power management unit,including but not limited to: the operating temperature of specificelectrical components, the ambient air temperature within a sealedportion of the fixture, the temperature of heat sinks or other thermalmanagement devices, or the ambient air temperature outside of thefixture. When measuring ambient air temperature outside of the fixture,it may be desirable to disregard the change in ambient temperatureattributable to the power dissipated by the fixture 100 itself. Theintelligent lighting system (PMU 130) may combine data on fixture powerconsumption with ambient temperature readings in order to produce a morereliable and accurate ambient temperature reading.

In some cases, it may be desirable to monitor temperature in anenvironment at a location physically separated from any light fixture100 deployed in the environment. In these cases, the temperature sensormay be contained in a remote module capable of communicating via awireless or wired network with the PMU 130, lighting fixture 100, and/orother devices in an intelligent lighting system. The remote temperaturesensor may be battery powered or may operate off of an AC or DC powerconnection.

The PMU 130 may record temperature data (e.g., from temperature sensor180) in the memory 134 for real-time analysis and for post-processingand historical data analysis. The temperature data may be recorded in adatabase (e.g., local memory 134 or remote memory accessible via thecommunications interface 160), and may be annotated with the locationwhere the reading was taken and the time at which it was taken. Thetemperature data may be analyzed to remove spurious readings, or to flagexcessively high or low readings for further processing or response. Thetemperature data may be displayed as a time-based graph, or as atwo-dimensional representation of the environmental layout with atemperature data overlay. Other building systems, including but notlimited to HVAC units, chillers, blowers, and heaters, may be configuredto act on real-time temperature data or alerts generated by anintelligent lighting system equipped with temperature sensors.Alternatively, the temperature data collected by the intelligentlighting system (PMU 130) may be exported in raw or processed form tocontrol systems responsible for managing these other building systemsfor the other building system control systems to analyze. Based ontemperature data it may also be possible to analyze and create visualrepresentations of airflow patterns within a facility, allowing foroptimized operation of HVAC and other related building systems.

CONCLUSION

While various inventive embodiments have been described and illustratedherein, those of ordinary skill in the art will readily envision avariety of other means and/or structures for performing the functionand/or obtaining the results and/or one or more of the advantagesdescribed herein, and each of such variations and/or modifications isdeemed to be within the scope of the inventive embodiments describedherein. More generally, those skilled in the art will readily appreciatethat all parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the inventive teachingsis/are used. Those skilled in the art will recognize, or be able toascertain using no more than routine experimentation, many equivalentsto the specific inventive embodiments described herein. It is,therefore, to be understood that the foregoing embodiments are presentedby way of example only and that, within the scope of the appended claimsand equivalents thereto, inventive embodiments may be practicedotherwise than as specifically described and claimed. Inventiveembodiments of the present disclosure are directed to each individualfeature, system, article, material, kit, and/or method described herein.In addition, any combination of two or more such features, systems,articles, materials, kits, and/or methods, if such features, systems,articles, materials, kits, and/or methods are not mutually inconsistent,is included within the inventive scope of the present disclosure.

The above-described embodiments can be implemented in any of numerousways. For example, the embodiments may be implemented using hardware,software or a combination thereof. When implemented in software, thesoftware code can be executed on any suitable processor or collection ofprocessors, whether provided in a single computer or distributed amongmultiple computers.

Further, it should be appreciated that a computer may be embodied in anyof a number of forms, such as a rack-mounted computer, a desktopcomputer, a laptop computer, or a tablet computer. Additionally, acomputer may be embedded in a device not generally regarded as acomputer but with suitable processing capabilities, including a PersonalDigital Assistant (PDA), a smart phone or any other suitable portable orfixed electronic device.

Also, a computer may have one or more input and output devices. Thesedevices can be used, among other things, to present a user interface.Examples of output devices that can be used to provide a user interfaceinclude printers or display screens for visual presentation of outputand speakers or other sound generating devices for audible presentationof output. Examples of input devices that can be used for a userinterface include keyboards, and pointing devices, such as mice, touchpads, and digitizing tablets. As another example, a computer may receiveinput information through speech recognition or in other audible format.

Such computers may be interconnected by one or more networks in anysuitable form, including a local area network or a wide area network,such as an enterprise network, and intelligent network (IN) or theInternet. Such networks may be based on any suitable technology and mayoperate according to any suitable protocol and may include wirelessnetworks, wired networks or fiber optic networks.

The various methods or processes outlined herein may be coded assoftware that is executable on one or more processors that employ anyone of a variety of operating systems or platforms. Additionally, suchsoftware may be written using any of a number of suitable programminglanguages and/or programming or scripting tools, and also may becompiled as executable machine language code or intermediate code thatis executed on a framework or virtual machine.

In this respect, various inventive concepts may be embodied as acomputer readable storage medium (or multiple computer readable storagemedia) (e.g., a computer memory, one or more floppy discs, compactdiscs, optical discs, magnetic tapes, flash memories, circuitconfigurations in Field Programmable Gate Arrays or other semiconductordevices, or other non-transitory medium or tangible computer storagemedium) encoded with one or more programs that, when executed on one ormore computers or other processors, perform methods that implement thevarious embodiments of the invention discussed above. The computerreadable medium or media can be transportable, such that the program orprograms stored thereon can be loaded onto one or more differentcomputers or other processors to implement various aspects of thepresent invention as discussed above.

The terms “program” or “software” are used herein in a generic sense torefer to any type of computer code or set of computer-executableinstructions that can be employed to program a computer or otherprocessor to implement various aspects of embodiments as discussedabove. Additionally, it should be appreciated that according to oneaspect, one or more computer programs that when executed perform methodsof the present invention need not reside on a single computer orprocessor, but may be distributed in a modular fashion amongst a numberof different computers or processors to implement various aspects of thepresent invention.

Computer-executable instructions may be in many forms, such as programmodules, executed by one or more computers or other devices. Generally,program modules include routines, programs, objects, components, datastructures, etc. that perform particular tasks or implement particularabstract data types. Typically the functionality of the program modulesmay be combined or distributed as desired in various embodiments.

Also, data structures may be stored in computer-readable media in anysuitable form. For simplicity of illustration, data structures may beshown to have fields that are related through location in the datastructure. Such relationships may likewise be achieved by assigningstorage for the fields with locations in a computer-readable medium thatconvey relationship between the fields. However, any suitable mechanismmay be used to establish a relationship between information in fields ofa data structure, including through the use of pointers, tags or othermechanisms that establish relationship between data elements.

Also, various inventive concepts may be embodied as one or more methods,of which an example has been provided. The acts performed as part of themethod may be ordered in any suitable way. Accordingly, embodiments maybe constructed in which acts are performed in an order different thanillustrated, which may include performing some acts simultaneously, eventhough shown as sequential acts in illustrative embodiments.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

What is claimed is:
 1. A lighting fixture to illuminate an environment,the lighting fixture comprising: A) a memory to store a first transferfunction mapping first ambient light levels at a first position withinthe environment to corresponding second ambient light levels at a secondposition within the environment; B) an ambient light sensor to measurean actual ambient light level at the first position within theenvironment; C) a processor, communicatively coupled to the memory andthe ambient light sensor, to determine: C1) an expected ambient lightlevel at the second position, based on the actual ambient light levelmeasured at the first position and the first transfer function stored inthe memory; and C2) a change in a light output of the lighting fixtureto provide a desired ambient light level at the second position, basedat least in part on the expected ambient light level at the secondposition; and D) at least one light source, communicatively coupled tothe processor, to generate the change in the light output of thelighting fixture so as to provide the desired ambient light level at thesecond position.
 2. The lighting fixture of claim 1, wherein theenvironment comprises at least one of: a warehouse, a cold-storagefacility, an office space, a retail space, an educational facility, anentertainment venue, a sports venue, a transportation facility, and acorrectional facility.
 3. The lighting fixture of claim 1, wherein thefirst position is at the lighting fixture and the second position is ata task height within the environment.
 4. The lighting fixture of claim1, wherein the memory is configured to store a plurality of transferfunctions, including the first transfer function, mapping ambient lightlevels at the first position within the environment to correspondingambient light levels at the second position within the environment,wherein each transfer function of the plurality of transfer functionscorresponds to a different state of the environment, and wherein thelighting fixture further comprises at least one of: E) a communicationsinterface to accept a user input selecting the first transfer functionfrom among the plurality of transfer functions; and F) a state parametersensor to provide a state parameter measurement used by the processor toselect the first transfer function from among the plurality of transferfunctions.
 5. The lighting fixture of claim 4, further comprising: G) areal-time clock, communicatively coupled to the processor, to provide atiming signal, wherein the processor is configured to select the firsttransfer function from among the plurality of transfer functions basedat least in part on the timing signal.
 6. The lighting fixture of claim1, wherein the processor is configured to determine at least one of: aportion of the actual ambient light level provided by the lightingfixture; and a portion of the actual ambient light level provided by oneor more light sources other than the lighting fixture.
 7. The lightingfixture of claim 1, wherein the ambient light sensor is configured tosense a wavelength of at least one spectral component of the actualambient light level, and wherein the processor is further configured todetermining a portion of the actual ambient light level based on thewavelength sensed by the ambient light sensor.
 8. The lighting fixtureof claim 1, wherein the processor is configured to control the at leastone light source to generate the change in the light output of thelighting fixture so as to provide the desired ambient light level at thesecond position by adjusting at least one of: an intensity of the lightoutput; a beam pattern of the light output; a direction of the lightoutput; a color of the light output; and a color temperature of thelight output.
 9. The lighting fixture of claim 1, further comprising: H)an occupancy sensor, communicatively coupled to the processor, to sensea presence of at least one occupant within the environment and toprovide an occupancy signal indicative of the at least one occupant,wherein the processor is configured to select the desired ambient lightlevel at the second position within the environment based at least inpart on the occupancy signal.
 10. The lighting fixture of claim 9,wherein the occupancy sensor is configured to sense at least one of: anumber of occupants within the environment, a location of the at leastone occupant within the environment, and a motion of the at least oneoccupant within the environment.
 11. The lighting fixture of claim 1,wherein the ambient light sensor is configured to measure a changedactual ambient light level at the first position after the change in thelight output of the lighting fixture generated by the at least one lightsource, and wherein the processor is configured to: C3) determine achanged expected ambient light level at the second position based on thefirst transfer function stored in the memory and the changed actualambient light level; C4) determine a difference between the changedexpected ambient light level and the desired ambient light level; andC5) adjust the transfer function stored in the memory based on thedifference between the changed expected ambient light level and thedesired ambient light level.
 12. A method of illuminating an environmentwith a lighting fixture, the method comprising: A) storing, in a memory,a first transfer function mapping ambient light levels at a firstposition within the environment to corresponding ambient light levels ata second position within the environment; B) measuring, with an ambientlight sensor, an actual ambient light level at the first position withinthe environment; C) determining an expected ambient light level at thesecond position, based at least in part on the first transfer functionstored in A) and the actual ambient light level at the first positionmeasured in B); D) determining a change in a light output of thelighting fixture to provide a desired ambient light level, based atleast in part on the expected ambient light level at the second positiondetermined in C); and E) causing the change in the light output of thelighting fixture determined in D) so as to provide the desired ambientlight level at the second position.
 13. The method of claim 12, whereinthe environment comprises at least one of: a warehouse, a cold-storagefacility, an office space, a retail space, an educational facility, anentertainment venue, a sports venue, a transportation facility, and acorrectional facility.
 14. The method of claim 12, wherein A) comprisesstoring a plurality of transfer functions, including the first transferfunction, mapping ambient light levels at the first position within theenvironment to corresponding ambient light levels at the second positionwithin the environment, wherein each transfer function of the pluralityof transfer functions corresponds to a different state of theenvironment, and wherein C) further comprises: C1) selecting the firsttransfer function from among the plurality of transfer functionsaccording to at least one of a user input and a measurement of a stateof the environment.
 15. The method of claim 14 wherein C1) comprisesselecting the first transfer function from among the plurality oftransfer functions based on at least in part on at least one of: a timeof day, a day of the week, and a day of the year.
 16. The method ofclaim 12, wherein the first position is at the lighting fixture and thesecond position is at a task height within the environment.
 17. Themethod of claim 12, wherein C) comprises: C1) determining a portion ofthe actual ambient light level provided by the lighting fixture; and C2)determining a portion of the actual ambient light level provided by oneor more light sources other than the lighting fixture.
 18. The method ofclaim 17, wherein B) comprises sensing a wavelength of at least onespectral component of the actual ambient light level, and wherein atleast one of C1) and C2) comprises determining the portion of the actualambient light level based on the wavelength sensed in B).
 19. The methodof claim 12, wherein E) comprises changing at least one of: an intensityof the light output; a beam pattern of the light output; a direction ofthe light output; a color of the light output; and a color temperatureof the light output.
 20. The method of claim 12, further comprising: F)sensing, with an occupancy sensor, a presence of at least one occupantwithin the environment; and G) selecting the desired ambient light levelat the second position within the environment based at least in part onthe presence of the at least one occupant sensed in F). 21-37.(canceled)